366 



ZOOLOGY. 



These projecting gills or branchiae in some continue through- 

 out life, as in the proteus, axolotl (Fig. 369), and siren. 

 But in most batrachia these branchiae soon wither away and 

 disappear, although the aquatic life continues, for the tadpole 

 has internal branchiae, like fishes, as well as external (Fig. 

 370) ; these fixed or internal branchiae in the tadpole are 



Fig. 369. The Axolotl j a Mexican Lizard. 



attached under the neck to cartilaginous arches belonging to 

 the hjoid bones, and are protected by the skin ; the water 

 reaches them by the cavity of the mouth, and escapes by one 

 or two orifices situated under the neck. In the tadpole of the 

 frog, the hind feet appear first, and they become of some 

 length before the fore feet are visible; these appear later 



Fig. 370. 



Fig. 371. 



Fig. 372. Fig. 373. Fig. 374. 



Figs. 370 374. Metamorphoses of the Tadpole of the Frog. 



(Fig. 372). In the salamanders it is the opposite ; finally, 

 in the siren the hind legs never appear. The tail of the 

 tadpole continues to grow in the salamander and proteus 

 with the rest of the body ; but in frogs and in many others 



